1. Field of the Invention
The present invention relates to use of a supplemental torque source to improve shift quality in a motor vehicle.
2. Description of the Related Art
Refer first to FIG. 1, an illustration of typical driven wheel torques during an automatic transmission upshift event, such as from first gear to second gear. (The upshift event begins at t=1.4 seconds on the horizontal axis and is complete at about t=2.0 seconds.) The curve reflecting a system with a torque converter shows a torque "hole" at about t=1.4 seconds due to engagement of the shifting clutch and subsequent transfer of torque from the offgoing to the oncoming friction element. Shudder-like oscillations, or "shuffle" in driven wheel torque then continue during the "intertia phase" of the shift until about t=2.0 seconds.
In order to reduce cost and improve the fuel efficiency of a motor vehicle with an automatic transmission, it has been proposed to remove the vehicle's torque converter. The resulting effect of subtracting the very significant damping effect of the torque converter is also shown in FIG. 1. The torque hole at t=1.4 seconds is larger, the oscillations up to t=2.0 seconds are larger, and very substantial oscillations in wheel torque continue beyond t=3.0 seconds. Obviously, much is lost in damping of wheel torque oscillations by removal of the torque converter.
Wheel torque oscillations are readily felt by the occupants of the vehicle. Therefore, a system which allows for removal of the torque converter for cost savings, particularly in a hybrid electric vehicle, and which can provide alternate damping for wheel torque oscillations will prove advantageous.